1. Field of the Invention
This invention relates to regulating the gas flow between a solid fuel gas generator and a combustor particularly by interposing an electronic valve control therebetween.
2. The Prior Art
Uncontrolled solid fuel gas generators experience significant variation in fuel flow rate due to thermal effects, progressive burning and throat deposition (in the outlet valve). This becomes a problem e.g. in rocket propulsion where one has a solid fuel gas generator in series with an outlet flow valve connected in turn, to a ducted (secondary) combustor or mounted in a rocket housing wherein the hot gas from the gas generator, mixes with an in-flowing oxidant such as air, burns and jets out of a nozzle aft in said housing to provide thrust for such rocket. In such case it is important to have a constant (rather than irregular) gas flow into the combustor for constant and predictable rocket propulsion. Conversely, it is often desired to vary the rocket's altitude and speed at certain points in its trajectory and it is therefore desirable to be able to vary the gas flow to the combustor and thus the propulsion of such rocket, in a controlled, predictable manner when desired.
To obtain the full potential performance of ducted rockets it is necessary to be able to regulate the fuel mass flow from gas generator to combustor. Unfortunately, there has been no simple way to directly measure the flow rate of the hot gases from gas generator to combustor. Attempts have been made in the prior art to indirectly measure and control such gas flow to combustors. Thus U.S. Pat. No. 4,355,663 (1982), U.S. Pat. No. 4,442,669 (1984) and U.S. Pat. No. 4,444,006 (1984), all to W. M. Burkes Jr. et al, relate to a nozzle/valve device for a ducted rocket motor in which a nozzle throat blockage element is moved into and out of such throat to vary gas flow therethrough from gas generator to combustor. These references teach the positioning of one pressure sensor, upstream of the blockage element, e.g., in the outlet of the gas generator thereto, which sensor is read by a logic circuit which operates the blockage element to control the gas flow through the throat to the combustor. However, such system relies on equations taking into account the known cross-sectional area of the throat, but doesn't take into account changes in such throat area when fuel deposits build up thereon, e.g., downstream of the pressure sensor so that the fuel flow data operating the logic and thus the fuel flow rate through the valve throat, becomes increasingly inaccurate with deposit build-up. Accordingly, the above three references disclose a system with one upstream pressure sensor that operates with crude fuel flow estimates so that an aerospace vehicle may not fly accurately and with a substantial loss of performance.
U.S. Pat. No. 4,574,586 to Gabrysch (1986) employs a nozzle valve throat blockage element between a gas generator upstream and a (secondary) combustor downstream, which choke operates in response to a temperature probe in the solid fuel grain of the gas generator to maintain the gas flow rate through such throat constant. Again, as fuel deposits build up in such throat, the choke reacts to progressively cruder fuel flow rate estimates.
Accordingly, there is a need and market for a fuel flow control valve that is accurate and durable and otherwise overcomes the above prior art shortcomings.
There has now been discovered a reliable control valve for a gas generator that accurately reads fuel flow therethrough even when fuel deposits occur in the throat thereof, to provide accurately controlled fuel flow to a secondary combustor, which flow can be held constant or varied as desired.